Method for bonding pile yarns onto rigid thermoplastics

ABSTRACT

Tufted substantially rigid thermoplastic articles useful as armrests, floor tiles, chair slats, and the like, are made by forming loops of a thermoplastic yarn upstanding from, and in contact with, a surface of the substantially rigid thermoplastic article and sonically bonding the yarn to the thermoplastic article at their points of contact.

United States Patent 1191 Carpenter 1*Aug. 19, 1975 METHOD FOR BONDING PILE YARNS ONTO RIGID THERMOPLASTICS [75] Inventor: Charles W. Carpenter, Wilmington,

Del.

[73] Assignee: Hercules Incorporated, Wilmington,

Del,

[ Notice: The portion of the term of this patent subsequent to Feb. 8, 1989,

has been disclaimed.

[22] Filed: July 26, 1972 [21} Appl. No.: 275,385

Related US. Application Data [63] Continuation of Ser. No. 888,708, Dec. 29, 1969, abandoned, which is a continuation-in-part of Ser. No. 780,038, Nov. 29, 1968, Pat. No. 3,640,786, which is a continuation-inpart of Ser. No. 731,221, May 22, 1968, abandoned.

[52] US. Cl 156/73.2; 156/177 51 Int. Cl. B32b 31/16 [58] Field of Search 156/73, 580, 177, 178

[56] References Cited UNITED STATES PATENTS 5/1953 Reinhardt 156/178 12/1969 Founder et a1. 156/73 Primary Examiner-Douglas J. Drummond Attorney, Agent, or FirmStanley A. Becker 5 7] ABSTRACT Tufted substantially rigid thermoplastic articles useful as armrests, floor tiles, chair slats, and the like, are made by forming loops of a thermoplastic yarn upstanding from, and in contact with, a surface of the substantially rigid thermoplastic article and sonically bonding the yarn to the thermoplastic article at their points of contact.

6 Claims, 1 Drawing Figure METHOD FOR BONDING PILE YARNS ONTO RIGID THERMOPLASTICS This application is a continuation of my prior application Ser. No. 888,708, filed Dec. 29, 1969, now abandoned, which in turn is a continuationin-part of my prior application Ser. No. 780,038, filed Nov. 29, 1968, now US. Pat. No. 3,640,786, which application, in turn, is a continuation-in-part of my prior application Ser. No. 731,221, filed May 22, 1968, now abandoned.

This invention relates to substantially rigid thermoplastic articles such as armrests, floor tiles, chair slats, and the like, having a portion of their surface covered with a tufted thermoplastic yarn and to a method and apparatus for making same.

When covering a substantially rigid article such as an armrest made of thermoplastic material with a tufted yarn, it is customary to tuft the yarn in a suitable backing material such as a nonwoven fabric and then cover the article with the tufted fabric with or without padding, as desired. This is a rather expensive operation since the tufted fabric must first be manufactured as by weaving wherein a face or pile yarn is woven into a backing, or by tufting wherein the pile yarn is needletufted through a backing at spaced points to form upstanding loops or tufts projecting from the face of the backing, and the tufted fabric then applied to or around the rigid article and secured thereto in some suitable manner.

The principal object of the present invention is the provision of a substantially rigid thermoplastic article having a portion of its surface covered with a tufted thermoplastic yarn and a process for making same which do not require the use of an intermediate backing material for the tufted portion, whereby a simpler, more economical product and process are provided. A further object of the invention is the provision of a substantially rigid thermoplastic article having a portion of the surface thereof covered with a tufted thermoplastic yarn wherein the tufted yarn is fusion bonded directly to the article, thus forming an integral part thereof. A still further object of the invention is the provision of such an article wherein fusion bonding of the yarn to the surface of the thermoplastic article is accomplished by sonic energy whereby a strong joint is formed and under conditions such that there is substantially no loss of orientation or crimp in the yarn between the bond joints.

In accordance with the invention, a series of U- shaped tufts or loops of oriented thermoplastic yarns is continuously formed on the surface of a substantially rigid thermoplastic article in a manner such that the legs of each tuft contact the surface of the article. Sonic energy is then applied at the points of contact of the yarn and article surface to heat and fusion-bond the yarn to the article at such points.

The tufted article of this invention is characterized in that the tufts or loops of yarn are fusion-bonded sonically directly to the thermoplastic article thereby elimi nating the need for an intermediate backing layer together with the added steps of forming a tufted backing layer and then securing it to the thermoplastic article. Moreover, by forming the bond between the article and the tufted yarn by sonically induced fusion-bonding only the bond points are caused to undergo any significant rise in temperature thereby avoiding any loss in the original level of orientation and crimp in the yarn between bond points. Because the orientation and crimp are thus preserved, the tufted yarn covering of the thermoplastic article has improved strength, resilience and covering power. This construction, moreover, provides substantial savings in pile yarn, eliminates the need for a backing member, does not involve the use of adhesives or solvents, and is runproof in that each tuft or loop is integrally fused to the article rather than tufted in a backing member.

As employed herein, the term fusion bonding normally denotes a bonding by melting the yarn and the surface of the article at the points of contact. However, the bond may comprise both fusion bonding and mechanical interlocking, wherein those portions of the bond receiving the most intense sonic excitation are in fact fused and the less excited portions are partially softened and plastically deformed. Where the two components that are to be joined, that is, the yarn and thermoplastic article, have more than a small difference in melting points, the bonding operation can be controlled to provide a high proportion of mechanical interlocking wherein a softened or melted portion of the lower melting component, the thermoplastic article, is deformed about and thus interlocks with the higher melting component, the yarn.

Ultrasonic welding devices usually comprise an alternating current generator having an output with a frequency in the ultrasonic range (for example, about 20,000 cps. a transducer assembly or sonic converter, and a sonic amplifier or horn. The transducer assembly comprises a transducer element which is preferably a piezoelectric crystal or a magnetostrictive device wherein the electrical output of the generator is converted by the endwise expansion and contraction of the transducer element in response to the varying voltage placed across it into mechanical vibrations at the same frequency as the electrical output of the generator. The sonic amplifier is connected to the output end of the transducer element and is operative to amplify the magnitude of the vibrations transmitted longitudinally therethrough.

In the fusion bonding of thermoplastic yarns to a substantially rigid thermoplastic article by the use of a sonic device of the above type, the horn is vibrated perpendicularly to the surface of the thermoplastic article and against the position of the thermoplastic yarns in contact therewith to effect alternately compression and relaxation of the thermoplastic materials at the points of contact at the indicated sonic frequency. This working of the thermoplastic materials generates heat at the points of contact between the thermoplastic elements sufficient to fuse the same without raising the temperature of the thermoplastic elements in areas outside of, or away from, the points of contact. The rate at which the temperature of a given mass of thermoplastic elements is raised and the level to which it is raised is determined by the pressure between the thermoplastic elements, which is determined in turn by the bias on the horn and the geometry of the horn tip, by the properties of the thermoplastic elements such as their thermal conductivity, modulus of elasticity and coefficient of friction, and by the sonic energy imparted to the thermoplastic elements as measured by the force, magnitude and velocity at which the horn tip is driven.

For a more detailed understanding of the present invention, reference is made to the accompanying drawings, in which:

FIG. 1 is a schematic view in perspective and partly broken away of an embodiment of the present invention.

FIG. 2 is a fragmentary view in perspective of a tufted thermoplastic article made by the embodiment of the invention shown in FIG. 1.

Referring now to FIG. 1, there is shown a sonic device which includes a housing 12 enclosing a sonic transducer (not shown) and a sonic amplifier 13 having a horn or sonic head 14 provided with a working surface 15. Since the details of the transducer are well known and do not constitute a critical part of the present invention, it is believed unnecessary to further describe them herein.

The sonic device 10 is carried by a support means comprising a bracket 16 on a bar 18 that is adapted to be moved endwise to move the sonic device 10 into and out of operative position relative to the work. The actuating means for the sonic device 10 comprises supporting means (not shown) mounting the bar 18 for endwise movement and a double acting pneumatic cylinder 19. The cylinder 19 can be operated by a cycling mechanism (not shown) which is adapted to provide an adjustable dwell of the bar 18 at both ends of its stroke and which, if desired, can also include actuating means for energizing the sonic transducer in timed relation to the movement of the sonic device 10. For example, in operation, the horn 14 may be moved into pressure engagement with the work and energized for a brief interval to effect a bond, after which there may be a brief dwell to allow partial cooling of the bond before the horn is moved out of engagement with the work. Alternatively, a preenergized or continuously energized sonic transducer can be used in which case the actuating means for energizing the sonic transducer will cause the same to be continuously energized during the complete cycle of operations. It will be evident, of course, that with the continuously energized sonic transducer bonding takes place only when it is in pressure engage ment with the work.

In the embodiment of the invention illustrated in the drawing, the substantially rigid thermoplastic article comprises an armrest 20 having an essentially flat surface 21. The armrest 20 is supported on a support member 22 fixed to a member 23 slidably mounted on a fixed base 24. The member 23 is adapted to be moved endwise in a fixed path on the base 24 by a traversing screw 25 rotated by suitable driving means (not shown). The member 22 and associated parts thus serve not only to support the armrest 20 but also to advance it to the bonding line, that is, the area or line 31 along which bonding takes place, as hereinafter described.

A tuft-forming mechanism for forming tufts in pile yarns is disposed above the member 22 and in advance or upstream of the horn 14. This mechanism comprises a looping bar 27 having a plurality of bores which define individual yarn tubes 28 through which the individual pile yarns 30 are threaded. The spacing between the tubes 28 determines the gauge or spacing between the pile yarns to be bonded to the surface of the article. Each of the bores 28 is dimensioned relative to the respective yarn 30 so as to impose a frictional drag upon the yarn threaded therethrough whereby the yarns will be pulled through the tubes 28 when the looping bar is moved away from the bonding line since the yarns are then anchored to the armrest by the bond that wasjust formed, but will be gripped by the bar 27 when it is moved toward the bonding line so that, insofar as it is not restrained by a tension exceeding the frictional grip thereon, it will be advanced with the bar 27. The bar 27 is carried by a bracket 32 which, in turn, is supported by supporting means (not shown) for reciprocation of the bar 27 in a direction to move the yarn output ends of the tubes 28 toward and from the bonding line 31.

In the operation of the apparatus, the pile yarns 30 are supplied from a suitable source (not shown) and are guided in a sheet-like array to and threaded through the bores 28 of the bar 27. In the starting point of a loop-forming cycle, each of the pile yarns 30 is secured to the armrest 20 along the bonded line 35 that was formed in the immediately preceding bonding operation, and the bar 27 is disposed in its bonding position, i.e., position C in FIG. 1 wherein the output ends of the tubes 28 are adjacent to the bonding line 31. The bar 27 is then retracted relative to the bonding line 31, that is, moved to position D in FIG. 1, so that with the yarns 30 secured to the armrest 20 at the bonded line 35, the yarns are pulled through the tubes 28.

Immediately upon completion of the tuft-forming cycle and as the bar 27 is being withdrawn, the horn 14 is raised from position B (shown in dot and dash lines), which is its bonding position, to position A, and the traversing screw 25 is actuated to advance the members 22 and 23 and the armrest 20 carried thereby endwise a distance equal to the desired tuft spacing, that is, the distance between successive bonded lines 35. The bar 27 is then advanced toward the bonding line 31 from position D to position C, during which movement the frictional engagement between the tubes 28 and the yarns 30 threaded therethrough causes the yarns 30 to be advanced with the tubes. Thus, the lengths of the yarns 30 between the output ends of the tubes 28 and the preceding bonded line 35, which are the lengths of yarn that were pulled through the tubes 28 when the bar 27 was retracted, are bowed upwardly from the armrest 20 to provide tufts of yarn, each of which is in the form of an inverted U upstanding from the surface of the armrest 20 with the one leg thereof secured at its end to the armrest 20 at the bonded line 35 that was just formed and the other end held adjacent to the armrest 20 at the bonding line 31 by the respective tube 28. Assuming that the yarns 30 are supplied in a substantially tensionfree condition or under a tension that is sufficiently low that it will not cause the yarns 30 to slip in the tubes 28, the length of the retracting stroke of the bar 27 determines the length of yarn that is drawn through the tubes 28 and thus the height of the tuft to be formed.

In the final step of the tuft-forming cycle, the horn 14 is lowered from position A to position B to engage the yarns and to force them against the surface of the armrest along the bonding line 31 under the predetermined bonding pressure and, if not preenergized or continuously energized, is energized to form a new bonded line 35.

Where intermittent energization is used, the cycling mechanism for the horn 14 is adjustable to provide for adjustment of the time that the sonic transducer is energized. The energization of the transducer is initiated as soon as the horn 14 has been moved to its bonding position, that is, to position B in FIG. 1, and may be initiated for example by switch means that responds to movement of the horn 14. With a horn that is biased to the bonding position, for example, by pneumatic means, when the horn 14 arrives at the end of the stroke, it also exerts a bias on the work and thus provides a bonding pressure which can be adjusted by adjustment of the line pressure. With a given bonding pressure, the length of time that the transducer must be energized to produce the desired bond is determined essentially by the energy input and the physical characteristics of the yarn and the armrest. The yarn beneath the working surface 15 of the horn 14 may be completely fused to the armrest so that it has in effect lost its identity as yarn, as illustrated at the bonded line 35 in FIG. 2, or may be surface bonded. At the same time, that portion of the surface of the armrest 20 immediately beneath the working surface 15 of the horn 14 is also heated and is displaced by the working face 15 to provide a groove 36.

In accordance with the above, the tufted article that is formed consists of a plurality of pile yarns 30 arranged in a spaced parallel manner lengthwise of the armrest 20 and fusion-bonded thereto at the bonded lines 35 extending transversely of the armrest 20 in a spaced parallel arrangement. For a uniform appearance and performance, the pile yarns 30 and the bonded lines 35 are both preferably equally spaced. Arranged in this manner, the pile yarns 3O define a series of rows of tufts 37 extending lengthwise of the armrest and consisting of the successive tufts formed in the individual pile yarns between the successive bonded lines 35 upon successive tuft-forming cycles, and series or rows of tufts extending transversely of the armrest and consisting of the tufts that are formed in the individual yarns in one tuft-forming cycle.

As illustrated in FIG. 2, each of the tufts 37 is upstanding from the upper surface of the armrest and has legs 38 spaced apart endwise of the armrest the distance through which the armrest is advanced upon each cycle, which is herein termed the tuft spacing, and secured at their ends to the armrest 20 along the bonded lines 35.

In the illustrated embodiment, the cycling mechanism for the horn 14 is also designed to provide an adjustable dwell of the horn 14 in the bonding position after the sonic transducer has been de-energized in order to provide for cooling and setting the bonds between the yarns and armrest.

One of the significant features of this invention is that the heating is localized and occurs essentially at the interfaces of the thermoplastic elements or in other words is focused precisely in the area in which the bond is formed. This not only minimizes power requirements, but also enables the materials to be brought very quickly to their bonding temperatures and minimizes the amount of heat that must be dissipated to reduce the temperature of the bond and thus set the same. Cooling and setting of the bond is accomplishedmore rapidly by the heat dissipation effect of the horn 14 which is not heated and thus remains cool during the bonding so that it can adsorb and thus conduct heat from the bond. The heat sink capacity of the horn 14 is sufficient to cool the bond to setting temperature within a very short dwell period after bonding. During this time, the horn 14 remains in its bonding position to hold the yarns 30 in place and thus to insure that they will set properly.

The crown or working surface 15 of the horn 14 is preferably as narrow as possible, for example, in the neighborhood of from about 0.010 to about 0.025 inch in width, in order to l) concentrate the sonic energy that is required to produce the desired bond and (2) to minimize the width of the bonded line 35. With the pile yarns 30 bonded to the armrest 20, the strength of the connection is not a function of the width of the bonded line 35. The appearance and performance of the armrest are also improved by a bonded line 35 of minimum width. Inasmuch as a length of the pile yarn 30 is consumed in forming the bonding line 35, a bonded line of minimum width represents a minimum loss of pile yarn and thus maximum coverage with a given quantity of yarn. There is also a reduced tendency for grinning, that is, for the bonded line 35 to show on the surface of the armrest, which is a condition that is particularly acute in forming the tufts on a curved surface.

The horn 14 is preferably elongated to provide a working surface 15 that is as long as possible consistent with uniform results. It is contemplated that articles wider than the width of a single horn can be produced by the use of a plurality of horns which may be arranged end-to-end or in another manner such as a staggered or steeped relation to minimize the effect of a gap between adjacent horns.

As mentioned above, it is preferred that the materials from which the yarn and article are formed be so chosen as to exhibit a minimum differential in their melting points, for example, less than about 20C., to insure a mutual interfusion of both the article and the yarn in order to form an optimum bond at a high production rate. Where the differential in melting points is relatively large, there may be incomplete fusion of the higher melting component or excessive fusion of the lower melting component.

Pattern or surface effects in tufted article may be achieved by cutting the tufts 37 such as by shearing to provide a cut pile effect or a mixed cut pile and loop pile effect. As herein used, it is contemplated that the term tuft will refer generically to pile such as the loops 37 as well as to pile which may be originally formed as loops but are either simultaneously or subsequently cut or sheared to provide cut pile or mixed cut pile and loop pile.

While the invention herein is illustrated and described with reference to its application for converting the exposed flat surface of a thermoplastic automotive armrest into a pile surface by the bonding thereto of pile yarns, it will be appreciated that it is applicable to the tufting of other thermoplastic articles such as, for example, floor tiles, chair slats, automotive panelling, and the like. Moreover, the thermoplastic article could be an injection molding, an extruded shape, or a thermoformed molding.

Any of the well-known synthetic yarns can be used in the present invention including those formed from thermoplastics such as polypropylene, polyethylene, polyesters, polyamides, polyacrylics, polyvinylchloride, polyvinylidene chloride, and so on. The thermoplastic article to which the tufting is to be applied can also be made from any of the well-known thermoplastic materials so long as the melting points of the thermoplastic article and yarn are sufficiently close to permit bonding them together in accordance with the invention. Moreover, the thermoplastic article may be solid throughout or may be foamed.

In order to satisfactorily tuft a thermoplastic article in accordance with the invention herein described, the surface of the article to be tufted should be rigid or substantially so. Thus, for example, if the underneath surface of the molding is ribbed, the support for the molding should be recessed to snugly receive the ribs so that the molding is fully supported along the bonding line.

While the invention is illustrated and described in connection with the tufting of flat surfaces of thermoplastic articles, it can also be used for the tufting of curved surfaces of such articles provided they are supported in a position such that the surface under the horn tip is normal to the vertical axis of the horn.

The following examples will serve to illustrate the present invention but are not to be taken as a measure of its limitation.

EXAMPLE 1 Utilizing equipment similar to that shown in FIG. 1, polypropylene multifilament yarn was bonded directly onto on 8 inch wide, 8 /8 inch long, one-fourth inch thick polypropylene plate in such a fashion as to convert a portion of the smooth surface into a tufted pile surface. The ultrasonic transducer assembly used was a commercially available standard unit operating at 20,000 c.p.s. and whose piezoelectric element was made of lead zirconate titanate. The booster attached to the transducer had a ratio of 2:l. The ultrasonic horn, made of titanium, was 7 /2 inches long with a rounded tip having sides at a 60 angle.

Fifty-nine yarn ends were fed from a creel to the looping bar. The bulked polypropylene pile yarn consisted of 120 filaments and the yarn denier was 2600. The yarn twist was 1 turn per inch. The one-fourth inch thick plate, previously cast from general purpose polypropylene resin was clamped to the flat support member which was intermittently indexed during the tufting operation to provide 7 rows per inch of looped pile yarn. In the transverse direction, the yarn gage, as determined by the hole spacing in the looping bar, was l/8 inch. The travel of the looping bar was adjusted so as to provide a pile height of approximately one-fourth inch.

Sonic bonding was accomplished in 0.3 sec. per weld line. The force at which the horn was held against the yarn was approximately 62 pounds. This force was maintained for a period of 0.1 sec. after deenergization of the horn.

At the completion of the tufting procedure, the dangling yarn ends adjacent to the initial and final weld lines were removed by cutting along the weld line. This left a tufted pile section approximately 6 inches by 7 /8 inches rising in a pleasing manner directly from the surface of the rigid plastic backing.

EXAMPLE 2 The apparatus and procedure of example 1 were used except that (l) the backing material was formed of foamed polypropylene and had a thickness of oneeighth inch and a density of about 26 lbs/cu. ft. In the tufting operation the horn was held against the yarn with a force of 35 pounds. The weld time was 0.5 second.

After removal from the support the samples were trimmed into squares approximately [2 inches on a side which were useful as rigid carpet tiles.

EXAMPLE 3 The apparatus of example 1 was used except that l the booster ratio was 1:1, (2) the ultrasonic horn was 3 inches long and had a 0.022 inch wide flat tip and sloping sides disposed at a angle, and (3) the support was one designed for use with long narrow strips.

Twelve ends of 3750/210 bulked continuous filament polypropylene yarn each having a twist of one turn per inch were bonded directly onto a 2 inch wide, 16 inch long, one-fourth inch thick backing plate made of the same material as in example 1. The backing plate was clamped to the support member which was intermittently indexed during the tufting operation to provide seven rows per inch of looped pile yarns. The yarn gage was five thirty-seconds inch and the pile height approximately one-fourth inch wide. Sonic bonding was accomplished in 0.3 seconds per weld line. The force at which the horn was held against the yarn was approximately eighty pounds. This force was maintained for a period of 0.2 seconds after deenergization of the horn.

After removal of the tufted strip from the support stray fibers along the sides were cut off. The resulting article was useful as tufted slats for outside folding aluminum chairs and similar applications.

What I claim and desire to protect by Letters Patent 1. In a method of covering the surface of an article with tufted yarn wherein the article is advanced in an endwise direction, a plurality of yarns are guided onto the surface of the article, loops are formed in the yarns upstanding from the surface of the article with a portion of each loop engaging the surface along a bonding line extending transversely of the path of advancement of said article; the improvement of which comprises:

providing a substantially rigid article of a thermoplastic material;

providing yarns of an oriented thermoplastic material; engaging the yams and thermoplastic article under pressure along a bonding line between a support and the working surface of a sonic device;

focusing the sonic device precisely along the bonding line to avoid loss in orientation level of the yarns between the bonding lines;

sonically fusion bonding the yarns to the thermoplastic article;

releasing the thermoplastic article and yarns from between said support and said sonic device; advancing the thermoplastic article a distance corresponding to the desired loop spacing; and repeating the above steps to cover the surface of said rigid article with tufted thermoplastic yarn.

2. A method in accordance with claim I wherein the sonic device is continuously energized.

3. A method in accordance with claim 1 wherein the sonic device is de-energized with the yarns and thermoplastic article in engagement under pressure between the support member and the working surface of the sonic device, and the engagement is maintained for a pre-determined time interval to provide for cooling and setting the bond between the yarns and thermoplastic article before release of the pressure thereon.

4. A method in accordance with claim 1 wherein a predetermined length of each yarn is fed upon each loop-forming cycle for controlling the height of the loops in the yarn.

5. A method in accordance with claim 1 wherein 6. A method in accordance with claim 1 wherein the guiding the yarns and forming the loops therein is pro vided by a bar having individual yarn tubes for each of the yarns through which the yarns are adapted to slide with a pre-determined frictional drag. 5

yarns are sonically fusion bonded and mechanically interlocked to the thermoplastic article. 

1. IN A METHOD OF CONVERTING THE SURFACE OF AN ARTICLE WITH TUFTED YARN WHEREIN THE ARTICLE IS ADVANCED IN AN ENDWISE DIRECTION, A PLURALITY OF YARNS ARE GUIDED ONTO THE SURFACE OF THE ARTICLE, LOOPS ARE FORMED IN THE YARNS UPSTANDING FROM THE SURFACE OF THE ARTICLE WITH A PORTION OF EACH LOOP ENGAGING THE SURFACE ALONG A BONDING LINE EXTENDING TRANSVERSELY OF THE PATH OF ADVANCEMENT OF SAID ARTICLE, THE IMPROVEMENT OF WHICH COMPRISES: PROVIDING A SUBSTANTIALLY RIGID ARTICLE OF A THERMOPLASTIC MATERIAL, PROVIDING YARNS OF AN ORIENTED THERMOPLASTIC MATERIAL, ENGAGING THE YARNS AND THERMOPLASTIC ARTICLE UNDER PRESSURE ALONG A BONDING LINE BETWEEN A SUPPORT AND THE WORKING SURFACE OF A SONIC DEVICE, FOCUSING THE SONIC DEVICE PRECISELY ALONG THE BONDING LINE TO AVOID LOSS IN ORIENTATION LEVEL OF THE YARNS BETWEEN THE BONDING LINES, SONICALLY FUSION BONDING THE YARNS TO THE THERMOPLASTIC ARTICLE, RELEASING THE THERMOPLASTIC ARTICLE AND YARNS FROM BETWEEN SAID SUPPORT AND SAID SONIC DEVICE, ADVANCING THE THERMOPLASTIC ARTICLE A DISTANCE CORRESPONDING TO THE DESIRED LOOP SPACING, AND REPEATING THE ABOVE STEPS TO COVER THE SURFACE OF SAID RIGID ARTICLE WITH TUFTED THERMOPLASTIC YARN.
 2. A method in accordance with claim 1 wherein the sonic device is continuously energized.
 3. A method in accordance with claim 1 wherein the sonic device is de-energized with the yarns and thermoplastic article in engagement under pressure between the support member and the working surface of the sonic device, and the engagement is maintained for a pre-determined time interval to prOvide for cooling and setting the bond between the yarns and thermoplastic article before release of the pressure thereon.
 4. A method in accordance with claim 1 wherein a predetermined length of each yarn is fed upon each loop-forming cycle for controlling the height of the loops in the yarn.
 5. A method in accordance with claim 1 wherein guiding the yarns and forming the loops therein is provided by a bar having individual yarn tubes for each of the yarns through which the yarns are adapted to slide with a pre-determined frictional drag.
 6. A method in accordance with claim 1 wherein the yarns are sonically fusion bonded and mechanically interlocked to the thermoplastic article. 